Data Reduction Frequently Asked Questions

Is a rv_step of 0.5 too wide for a precise RV extraction? What would a good step size be?


The choice of the rv_step default is a compromise between precision and speed. The recommendation is to use a good guess for rv_center, select the right rv_range to include the whole line, and change rv_step to optimise results, considering the trade-off between precision and efficiency. 0.5 km/s is the size of an ESPRESSO pixel when measured in RV. Using a step larger than this value is equivalent to using fewer pixels to sample the FWHM of the line; on the other hand, using a smaller pixel can lead to a gain in RV precision, but it will depend on the specific case.